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In this image provided by NASA, a robotic arm from NASA's Mars Exploration rover Spirit is shown on the 1,277th Martian day in this Aug. 6, 2007. In a rare move, NASA reversed its earlier decision to cut funding to the twin rovers.

LOS ANGELES — NASA has no plans to turn off either of the healthy twin Mars rovers to make up for cost overruns faced by a big new rover slated to fly to the Red Planet next year, the space agency said Tuesday.

In a rare move, NASA said it rescinded a letter sent last week to the Jet Propulsion Laboratory in Pasadena that directed budget cuts to the Mars exploration program, including a $4 million reduction from the rovers project.

The action comes a day after scientists involved in the rovers mission said they would need to hibernate the rover Spirit and limit the duties of its twin, Opportunity, to fulfill NASA's budget cut.

The solar-powered rovers landed on Mars in 2004 and have long outlasted their planned three-month mission. They have impressed scientists and the public with findings of geologic evidence that water once flowed at or near the surface of ancient Mars.

"All elements of the Mars Exploration Program will operate under their previous program guidance as if the letter was never sent," NASA spokesman Dwayne Brown said in a statement.

NASA Administrator Michael Griffin did not review the letter, sent by James Green, who leads the agency's planetary science division.

"Dr. Griffin did not know beforehand that Dr. Green sent the letter, nor did Dr. Green obtain explicit approval from Dr. Griffin to send the letter," Brown said.

Rover principal investigator Steve Squyres of Cornell University said a cut would have devastated the rovers. Mission team members were considering contingency plans to put Spirit to sleep for several months and curtail Opportunity's exploration.

"Our job is to operate the rovers with the resources that NASA gives us," Squyres said.

With the cuts to the Mars program restored, NASA still needs to find funding to cover the Mars Science Laboratory, a Hummer-size next-generation rover scheduled to launch next year.

Engineers had to redesign the protective heat shield on the robot after tests showed it would not survive entry to the planet's atmosphere. The extra work is expected to add $20 million to $30 million to the $1.8 billion price tag, already $165 million over budget.